This study will illuminate the capabilities of the human larynx and inform the relationship between voice production and perception. The long term goal of this research is to inform and provide new directions for transgender (TG) voice care, thereby improving the lives of TG people who feel their voice is a great obstacle to living as their preferred gender. Incomplete gender presentation can negatively impact the TG individual's job opportunities, relationships, and social acceptance. Results of this project will advance an aspect of gender transition vital to being accepted as one's preferred gender and living a successful, healthy life. Knowledge about how the male-to-female transgender (MTF) larynx overcomes constraints of biological anatomy, as well as which voice parameters contribute to listener's perceptions of gender, can be used to develop standards for voice care and feminization therapy. Like voice therapy for other populations, TG voice therapy should be grounded in knowledge of the vocal mechanism of the speaker. It should not resort, as it currently does, to establishing acoustic goals based exclusively on differences between normative values of two gender groups and assumed gender perception boundaries. Contrary to current thinking in TG voice care, preliminary data indicate that MTF voice is not necessarily an average of male and female voice, and there are physiological distinctions between passing and not-passing MTF speakers. These data suggest that clinical decision making should consider that MTF speakers who pass as female use a glottal management technique unique from non-transgender males or females. Airflow and EGG signals will be simultaneously collected and aligned to determine how the passing MTF voice achieves a female-sounding voice with biologically male anatomy. For the first time, the mechanism of passing MTF voice physiology will be quantified in detail and compared to non-TG male and female speakers, as well as MTF speakers who do not achieve female-sounding voice. One hundred listeners, from within and outside of the Gay-Lesbian-Bisexual-Transgender (LGBT) community, will judge the gender of reiterative speech samples from male, female, and male-to-female (MTF) speakers. The listener's perceptions will be used first to divide the MTF group into those who pass as female and those who do not so that glottal measures from these two groups can be compared to each other, and to the non-transgender groups of males and females. The perceptual ratings then will be entered in a regression model with other acoustic, articulatory and prosodic variables (Mean F0, spectral envelope decay, formants 1-3, intonation shifts) in order to develop a comprehensive model useful for predicting confidence that a speaker will be perceived as their preferred gender. It is hypothesized that while F0 is a strong predictor, airflow and glottal closure parameters will improve the fit of the model for gender perception.